Currently two animal protocols (one mouse and one rabbit) are ongoing. The purpose of the mouse studies is to understand the biology of the limbal epithelial cells after limbal tranplantation. The mouse studies will be focused on limbal stem cell biology and immunlogy taking advantage of various transgenic strains. Currently ongoing studies focusses on the long-term survival of transplantated limbal stem cells in transgenic animal models. Using confocal techniques and immunolabelling the presence of the long term survival of these cells in a tranplanted environment would be looked in to in greater detail. This has importance in the understanding whether the cultured stem cell transplantation in the long term has any role in maintaining clear ocular surface. The plasticity of limbal stem cells in various stages of development will also be studied. Using gene expression studies, attempts will be made to determine the factors that are important for maintaining "stemness". Human studies evaluating the continued presence of donor limbal stem cells is being done in parallel with the animal studies. In these studies limbal corneal rims from patients who underwent previous stem cell allogeneic limbal stem cell transplants and then a penetrating keratoplasty have been analysed. The presence or absence of donor stem cells is being evaluated using microsatellite techniques. Other human tissue would look in the ultrastructural changes in the cornea following cultured limbal transplants on different substrates.Initial results have confirmed the validity of the technique being employed and donor stem cells can remain present for years after transplant. These findings will have therapeutic implications since patients receiving allogeneic transplants must be immunosuppressed. The focus of the rabbit studies is to understand and prevent immunologic rejection of the transplanted limbal stem cells using donor tissue manipulation and local immunosuppression including sustained release implants. Studies currently in progress involve tissue engineering using cultured corneal epithelial cells for the treatment stem cell deficiency. These latter studies will likely provide the basis for future clinical studies using cultured corneal epithelial cells.